This sort of follows on from having helped with the divmod10() thread: divmod10() : a fast replacement for /10 and %10 (unsigned) - #34 by TCWORLD - Libraries - Arduino Forum I have a program which does a large number of division by 3 and division by 5. The built in functions for division are fairl…

divu5() and divu3(). Fast replacements for unsigned division by 3, 5, 6, 10, 15

TCWORLD June 18, 2013, 4:12pm 4

One library for thee.

EDIT:
Fixed a glitch with n=0xFFFF